Charge pump for generating arbitrary voltage levels

ABSTRACT

A charge pump for generating an arbitrary voltage level includes “M” pieces of pump units PU i  and “M+1” pieces of first switches S j . The pump unit PU i  includes a first terminal N i,1  coupled to a reference voltage V i,1 , a second terminal N i,2  coupled to a reference voltage V i,2 , a third terminal N i,3 , a fourth terminal N i,4  and at least one capacitor C i . C i  is charged by V i,1  and V i,2  during a first period, and a voltage is provided from N i,4  by C i  according to a voltage at N i,3  during a second period. The first switch S j  is adapted for electrically connecting the first terminal and the second terminal during the second period. The first and second terminals of S k  is coupled to N k−1,4  and N k,3 , respectively. The first terminal of S i  receives the input voltage and the second terminal of S M+1  outputs the output voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 94121792, filed on Jun. 29, 2005. All disclosure of the Taiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to charge pumps, and particularly to a charge pump for generating arbitrary voltage levels.

2. Description of Related Art

In an electronic circuit, power source voltages of different levels are often required; therefore, a charge pump circuit for generating power source voltages of different levels with the present power source voltage is usually equipped therein.

FIG. 1A is a circuit diagram of a conventional charge pump. FIG. 1B is a timing sequence diagram of control signals for illustrating the charge pump according to FIG. 1A. Referring to FIGS. 1A and 1B together, the charge pump has five transistors; the control signals ph₁ and ph₂ are opposite in phase, wherein it is V_(dd) when at high voltage level and it is zero when at low voltage level.

During the charging period (CP) of a capacitor C1, the control signals ph₁ and ph₂ are respectively at low voltage level and high voltage level. Therefore, the transistors M₁ and M₃ are turned off while the transistors M₀, M₂ and M₄ are turned on. The voltage at the terminal of the capacitor C₁ which is coupled to the control signal ph₁ is zero. The power source voltage V_(dd) charges the capacitor C₁ via the transistor M₀ until the voltage difference between the two terminals is V_(dd)−V_(t); wherein, V_(t) is a threshold voltage of the transistors M₀ to M₄.

During the pumping period (PP) of the capacitor C₁, the control signals ph₁ and ph₂ are respectively at high voltage level and low voltage level, therefore the transistors M₁ and M₃ are turned on while the transistors M₀, M₂ and M₄ are turned off. The voltage at the terminal of the capacitor C₁ which is coupled to the control signal ph1 is V_(dd). Because a charge of voltage difference of V_(dd)−V_(t) has been stored during the charging period CP, the voltage of another terminal of the capacitor C₁ will raise up to 2V_(dd)−V_(t). Also, the voltage of a terminal of a capacitor C₂ which is coupled to the control signal ph₂ is zero, therefore the voltage 2V_(dd)−V_(t) of another terminal of the capacitor C₁ charges the capacitor C₂ via the transistor M₁ until the voltage difference between the two terminals of the capacitor C₂ is 2V_(dd)−2V_(t).

Then, by analyzing the voltage variation according to the foregoing method, it can be known that the output voltage V_(o) from the charge pump is 5×(V_(dd)−V_(t)). Similarly, if the charge pump has N transistors, the output voltage is N×(V_(dd)−V_(t)). It can be known from the formula of the output voltage V_(o) that the charge pump can only generate some power source voltages having certain voltage levels.

SUMMARY OF THE INVENTION

In view of the above, an object of the present invention is to provide a charge pump for generating arbitrary voltage levels.

The invention provides a charge pump for generating an output voltage having arbitrary voltage levels according to the input voltage. The charge pump includes “M” pieces of pump units PU_(i) and “M+1” pieces of first switches S_(j); wherein, PU_(i) represents the “i^(th)” pump unit, “i” is an integer greater than 0 and smaller than or equal to “M”, “M” is an integer greater than or equal to 1; S_(j) represents the “j^(th)” first switch, “j” is an integer greater than 0 and smaller than or equal to “M+1”.

The pump unit PU_(i) includes a first terminal N_(i,1) coupled to a reference voltage V_(i,1), a second terminal N_(i,2) coupled to a reference voltage V_(i,2), a third terminal N_(i,3) , a fourth terminal N_(i,4) and at least one capacitor C_(i). Wherein, N_(i,1), N_(i,2), N_(i,3), and N_(i,4) respectively represent the first terminal, the second terminal, the third terminal and the fourth terminal of the PU_(i); and C_(i) represents an internal capacitor of the PU_(i). The pump unit PU_(i) is adapted for charging C_(i) with V_(i,1) and V_(i,2) in a first period and providing a voltage to N_(i,4) in a second period according to the voltage level of N_(i,3).

The first switch S_(j) includes a first terminal and a second terminal and is adapted for electrically connecting the first terminal and the second terminal during the second period. The first terminal of S₁ receives the input voltage and the second terminal of S₁ is coupled to N_(1,3); the first terminal of S_(k) is coupled to N_(k−1,4) and the second terminal of S_(k) is coupled to N_(k,3); the first terminal of S_(M+1) is coupled to N_(M,4) and the second terminal of S_(M+1) outputs the output voltage, wherein “k” is an integer greater than 1 and smaller than or equal to “M”.

The invention employs a multi-stage pump units coupled in series with the adjustable voltages of the input terminal and the pump units; therefore, the charge pump according to the invention can generate arbitrary voltage levels.

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a circuit diagram of a conventional charge pump.

FIG. 1B is a timing sequence diagram of control signals illustrating the charge pump according to FIG. 1A.

FIG. 2 is a circuit diagram of a charge pump in accordance with an embodiment of the invention.

FIGS. 3A and 3B are equivalent circuit of the charge pump shown in FIG. 2 respectively during the first and the second periods, wherein the charge pump is for generating a positive voltage.

FIGS. 4A and 4B are equivalent circuit of the charge pump shown in FIG. 2 respectively during the first and the second periods, wherein the charge pump is for generating a negative voltage.

DESCRIPTION OF THE EMBODIMENTS

In order to more clearly illustrate the embodiment of the invention, a charge pump composed of three pump units is exemplified herein; those who are skilled in related art may obtain charge pumps composed of one or more pump units in accordance with the invention.

FIG. 2 is a circuit diagram of a charge pump in accordance with an embodiment of the invention. Referring to FIG. 2, a charge pump 20 includes three pump units PU₁, PU₂, PU₃, four first switches S₁, S₂, S₃, S₄ and an output capacitor C_(L). Each of the pump units PU_(i) includes a first terminal N_(i,1), a second terminal N_(i,2), a third terminal N_(i,3), a fourth terminal N_(i,4), two second switches SW_(i,1), SW_(i,2) and a capacitor C_(i), wherein, “i” is an integer and 0<i≦3. The first terminal N_(i,1) is coupled to a reference voltage V_(i,1) and a second terminal N_(i,2) is coupled to a reference V_(i,2).

Only the pump unit PU₁ will be illustrated as an example herein; the architecture of other pump units is similar to that of the pump unit PU₁ and thus description is omitted. The pump unit PU₁ includes a first terminal N_(i,1) coupled to a reference voltage V_(1,1), a second terminal N_(i,2) coupled to a reference voltage V_(1,2), a third terminal N_(1,3), a fourth terminal N_(1,4), a second switch SW_(1,1), a second switch SW_(1,2) and a capacitor C₁; wherein, the first terminal and the second terminal of the second switch SW_(1,1) are respectively the first terminal N_(1,1) and the fourth terminal N_(1,4) of the pump unit PU₁; the first terminal and the second terminal of the second switch SW_(1,2) are respectively the third terminal N_(1,3) and the second terminal N_(1,2) of the pump unit PU₁; and the first terminal and the second terminal of the capacitor C₁ are respectively coupled to the second terminal of the second switch SW_(1,1) and the first terminal of the second switch SW_(1,2).

First switches S₁, S₂, S₃ and S₄ are coupled respectively to the corresponding pump units PU₁, PU₂ and PU₃. The first terminal of the first switch S₁ is adapted for receiving an input voltage V_(i) and the second terminal of the first switch S₁ is coupled to the third terminal N_(1,3) of the pump unit PU₁. The first terminal and the second terminal of the first switch S₂ are respectively coupled to the fourth terminal N_(1,4) of the pump unit PU₁ and the third terminal N_(2,3) of the pump unit PU₂. The first terminal and the second terminal of the first switch S₃ are respectively coupled to the fourth terminal N_(2,4) of the pump unit PU₂ and the third terminal N_(3,3) of the pump unit PU₃. The first terminal of the first switch S₄ is coupled to the fourth terminal N_(3,4) of the pump unit PU₃ and the second terminal of the first switch S₄ outputs the output voltage V_(o).

The timing sequence diagram of the control signals ph₁ and ph₂ of the charge pump 20 shown in FIG. 2 may be the same as that shown in FIG. 1B. Referring to ph₁ and ph₂ which are opposite in phase, the charge pump 20 makes the second switches SW_(1,1), SW_(1,2), SW_(2,1), SW_(2,2), SW_(3,1) and SW_(3,2) (all of which are controlled by control signal ph₁) turn on, and the first switches S₁, S₂, S₃ and S₄ (all of which are controlled by control signal ph₂) turn off during the first period; and the second switches SW_(1,1), SW_(1,2), SW_(2,1), SW_(2,2), SW_(3,1) and SW_(3,2) turn off, and the first switches S₁, S₂, S₃ and S₄ turn on during the second period. Herein, when at high levels the voltages of the control signals ph₁ and ph₂ are not necessary to be V_(dd), and when at low voltage levels the voltages of the control signals ph₁ and ph₂ are not required to be zero as long as the voltages at high levels can control the switches to be turned on and at low levels the switches are turned off. Furthermore, considering the design of the switches, it is not a must to turn on the switches with a high level and to turn off the switches at a low level. Such switches may be constituted of NMOS transistors, PMOS transistors, transmission gates or a combination of such components.

Moreover, a retaining circuit (e.g. an output capacitor C_(L)) is coupled between the second terminal of the first switch S₄ and grounding for retaining the voltage level of output voltage V_(o) when the first switch S₄ is turned off. Herein, other retaining circuit design can also be adopted for obtaining similar performance. As arbitrary voltages, the input voltage V_(i) and all the reference voltages V_(1,1), V_(1,2), V_(2,1), V_(2,2), V_(3,1) and V_(3,2) can be provided by a power source voltage or a voltage regulator.

FIGS. 3A and 3B are equivalent circuit of the charge pump 20 shown in FIG. 2 respectively during the first and the second periods. Wherein, the charge pump 20 is for generating a positive voltage. To simplify the illustration, the unnecessary components, terminals and nodes are not shown in the figures.

Referring to FIG. 3A, in the first period, the second switches SW_(i,1) and SW_(i,2) are turned on, and the first switch S_(j) is turned off. The equivalent circuit of the charge pump 20 is as shown in FIG. 3A. The charge pump 20 charges the capacitor C_(i) according to reference voltages V_(i,1) and V_(i,2). As an example, suppose V_(i,1)>V_(i,2), namely V_(1,1)>V_(1,2), V_(2,1)>V_(2,2), and V_(3,1)>V_(3,2), then the capacitors C₁ to C₃ are respectively charged to have voltage differences ΔV₁ to ΔV₃, wherein ΔV₁=V_(1,1)−V_(1,2), ΔV₂=V_(2,1)−V_(2,2) and ΔV₃=V_(3,1)−V_(3,2). Thus, the first period is a charging period.

Referring to FIG. 3B, in the second period, the second switches SW_(i,1) and SW_(i,2) are turned off, and the first switches S_(j) is turned on. The equivalent circuit of the charge pump 20 is as shown in FIG. 3B. Herein, the pump unit PU_(i) makes the capacitor C_(i) provide voltage to the fourth terminal N_(i,4) according to the voltage level of the third terminal N_(i,3). For example, the voltage of the fourth terminal N_(1,4) of the pump unit PU₁ is the sum of the voltage V_(i) of the third terminal N_(1,3) and the voltage difference ΔV₁ of the capacitor C₁. Thus, the output voltage is V_(o)=V_(i)+ΔV₁+ΔV₂+ΔV₃, wherein ΔV₁>0, ΔV₂>0, ΔV₃>0, and the range of voltage increase can be adjusted via designing V_(i) and ΔV_(i). Thus, the second period is a pumping period, and a positive voltage is produced.

In the first embodiment, V_(i,1)=V_(dd) and V_(i,2)=0, namely the terminals of all pump units PU₁ to PU₃ receive voltage V_(dd) while the second terminals are grounded, thus ΔV₁=ΔV₂=ΔV₃ and the output voltage is V_(o)=V_(i)+3V_(dd). However, the aforementioned charge pump 20 is only a special example in accordance with the invention. Practically, the invention may also connect with multiple pump units in series to increase voltage for obtaining an output voltage at arbitrary positive voltage level. For example, if a charge pump according to the invention connects with “M” pieces of pump units in series which needs “M+1” pieces of first switches, the output voltage is V_(o)=V_(i)+M×V_(dd). Accordingly, the value of “M” and the input voltage V_(i) can be determined in accordance with the requirement of the output voltage. Generally, the input voltage V_(i) is lower than the power source voltage V_(dd).

In another embodiment, V_(i,1)=V_(i) and V_(i,2)=0, thus ΔV_(i)=V_(i). If a charge pump connects with M pieces of pump units in series, the output voltage is V_(o)=V_(i)+M×V_(i).

FIGS. 4A and 4B are equivalent circuit of the charge pump 20 shown in FIG. 2 respectively during the first and the second periods; wherein, the charge pump 20 is for generating a negative voltage. Referring to FIGS. 4A and 4B, the equivalent circuit is respectively similar to that in FIGS. 3A and 3B. The difference is that the reference voltages V_(i,1) are smaller than V_(i,2), namely V_(1,1)<V_(1,2), V_(2,1)<V_(2,2) and V_(3,1)<V_(3,2). Hence, the capacitors C₁ to C₃ are respectively charged to have voltage differences ΔV₁ to ΔV₃, wherein ΔV₁=V_(1,1)−V_(1,2), ΔV₂=V_(2,1)−V_(2,2) and ΔV₃=V_(3,1)−V_(3,2). However, the polarities of the capacitors C₁ to C₃ in FIG. 4A are opposite to those of the capacitors C₁ to C₃ in FIG. 3A. Therefore, as shown in FIG. 4B, in the second period, the output voltage is V_(o)=V_(i)+ΔV₁+ΔV₂+ΔV₃, wherein ΔV₁<0, ΔV₂<0, ΔV₃<0, and a negative voltage is produced. In an aspect of the embodiment, V_(i,1)=0 and V_(i,2)=V_(dd), thus the output voltage V_(o)=V_(i)−3V_(dd). In another aspect of the embodiment, V_(i,1)=V_(i) and V_(i,2)=0, thus the output voltage V_(o)=V_(i)−3V_(i). Of course, the invention may also connect with multiple pump units in series to decrease voltage for obtaining an output voltage at arbitrary negative voltage level.

In summary, the charge pump according to the present invention employs a plurality of pump units connected in series incorporating with adjustable input voltage V_(i) and the adjustable reference voltages of all the pump units. Thus, arbitrary positive/negative voltage levels can be obtained.

It should be noted that specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize that modifications and adaptations of the above-described preferred embodiments of the present invention may be made to meet particular requirements. This disclosure is intended to exemplify the invention without limiting its scope. All modifications that incorporate the invention disclosed in the preferred embodiment are to be construed as coming within the scope of the appended claims or the range of equivalents to which the claims are entitled. 

1. A charge pump adapted for generating an output voltage having an arbitrary voltage level according to an input voltage and at least one reference voltage, the charge pump comprising: M pieces of pump units PU_(i), wherein PU_(i) represents the i^(th) pump unit, “i” being an integer which is greater than 0 and smaller than or equal to M, M being an integer which is greater than or equal to 1, the pump unit PU_(i) comprising: a first terminal N_(i,1), coupled to a reference voltage V_(i,1), wherein N_(i,1) represents the first terminal of PU_(i) and V_(i,1) represents the voltage coupled to N_(i,1); a second terminal N_(i,2), coupled to a reference voltage V_(i,2), wherein N_(i,2) represents the second terminal of PU_(i) and V_(i,2) represents the voltage coupled to N_(i,2); a third terminal N_(i,3), wherein N_(i,3) represents the third terminal of PU_(i); a fourth terminal N_(i,4), wherein N_(i,4) represents the fourth terminal of PU_(i); and at least one capacitor C_(i), wherein C_(i) represents an internal capacitor or capacitors of PU_(i), the pump unit PU_(i) being adapted for charging C_(i) with V_(i,1) and V_(i,2) in a first period, and providing a voltage to N_(i,4) according to the voltage level of N_(i,3) in a second period; and “M+1” pieces of first switches S_(j), wherein S_(j) represents the j^(th) first switch, “j” being an integer which is greater than 0 and smaller than or equal to “M+1”; S_(j) is adapted for electrically connecting the first terminal and the second terminal thereof during the second period, wherein the first terminal of S₁ receives the input voltage and the second terminal of S₁ is coupled to N_(1,3); the first terminal of S_(k) is coupled to N_(k−1,4) and the second terminal of S_(k) is coupled to N_(k,3); the first terminal of S_(M+1) is coupled to N_(M,4) and the second terminal of S_(M+1) outputs the output voltage, wherein “k” is an integer which is greater than 1 and smaller than or equal to “M”.
 2. The charge pump as claimed in claim 1, wherein the first switch S_(j) is one of a group consisting of NMOS transistors, PMOS transistors, transmission gates or a combination of such components.
 3. The charge pump as claimed in claim 1, wherein the pump unit PU_(i) further comprises: a second switch SW_(i,h), SW_(i,h) representing the “h^(th)” second switch of the pump unit PU_(i), wherein “h” is 1 or 2, for electrically conducting the first terminal and the second terminal during the first period, wherein the first terminal of SW_(i,1) is N_(i,1), the second terminal of SW_(i,1) is coupled to the first terminal of C_(i) and the first terminal of SW_(i,2) is coupled to the second terminal of C_(i); the second terminal of SW_(i,2) is N_(i,2); the first terminal of C_(i) is N_(i,4); and the second terminal of C_(i) is N_(i,3).
 4. The charge pump as claimed in claim 3, wherein V_(i,1)>V_(i,2).
 5. The charge pump as claimed in claim 3, wherein V_(i,1)<V_(i,2).
 6. The charge pump as claimed in claim 3, wherein the second switch SW_(i,h) is one of a group consisting of NMOS transistors, PMOS transistors, transmission gates or a combination of such components.
 7. The charge pump as claimed in claim 1, further comprising a voltage regulator coupled to the first terminal of the first switch S₁ for providing and adjusting the input voltage.
 8. The charge pump as claimed in claim 1, wherein the input voltage is provided by a power source voltage or a ground voltage.
 9. The charge pump as claimed in claim 1, wherein the reference voltages V_(i,1) and V_(i,2) are provided by a power source voltage or a voltage regulator.
 10. The charge pump as claimed in claim 1, further comprising a retaining circuit coupled to the second terminal of the first switch S_(M+1) for retaining the output voltage.
 11. The charge pump as claimed in claim 10, wherein the retaining circuit comprises an output capacitor, the output capacitor being coupled between the second terminal of the first switch S_(M+1) and a ground. 